Heat generated by lighting of an arc tube rises toward the opposite side of gravity in the arc tube, whereby the surface temperature of the top portion of the arc tube is higher than the bottom portion. The arc tube temperature and arc tube product life are strongly related, and proper management of arc tube temperature is therefore of key importance. To extend the product life of an arc tube, it is important to reduce the temperature difference between the top portion and bottom portion of the arc tube. Accordingly, cooling preferably focuses on the top portion of an arc tube in a state in which a device that is provided with a lamp unit is installed on a floor surface (hereinbelow, a “standing state”).
Based on these circumstances, as the cooling means of the arc tube, a device equipped with a lamp unit is provided with one jet such that a cooling airflow is blown against the top portion of the arc tube in a predetermined installation state. With this type of cooling means, however, if the device in the standing state is turned upside down and installed on a ceiling (hereinbelow referred to as a “suspended state”), the cooling airflow from the jet is blown chiefly against the bottom portion of the arc tube, resulting in a problem in which the temperature difference between the top portion and bottom portion of the arc tube is actually increased.
As a technique for solving this problem, a configuration has been proposed in which a cooling airflow guide plate that can move according to the installed state and that can switch the direction of flow of the cooling airflow is provided in the cooling airflow jet such that the cooling airflow is blown against the top portion of the arc tube whether in a standing state or in a suspended state (see JP-A-2006-091132 (hereinbelow referred to as Patent Document 1)).
Although not a technique for solving the problem described above caused by the installation state, JP-A-2002-352604 (hereinbelow referred to as Patent Document 2) discloses the provision of front ventilation ports above and below the front portion of a reflector and the arrangement of a cooling fan to confront each front ventilation port. Cooling air is then introduced to the inner space of the reflector from each front ventilation port to cool a light-source lamp, and the warm air in the inner space of the reflector is then exhausted outside the reflector from a rear ventilation port provided in the rear portion of the reflector.
However, the method disclosed in Patent Document 1only lowers the temperature of the top portion of the arc tube, and maintaining the temperature of the top portion and bottom portion of the arc tube within a prescribed temperature range still remains a problem. The problem therefore arises that the temperature difference between the upper and bottom portions of the arc tube differs depending on the installation orientation.
Because this is a technology in which the cooling airflow guide plate can be moved according to the installation state of the device, the construction is complex. In addition, the problem arises in which the adherence of extraneous matter to the movable mechanism of the cooling airflow guide plate prevents satisfactory switching of the airflow direction realized by the cooling airflow guide plate.
In Patent Document 2, moreover, there is absolutely no disclosure of the idea of guiding the cooling airflow into the reflector such that the cooling airflow concentrates at the top portion and bottom portion of the light source. On the contrary, paragraphs and of this document describe the effective ventilation of the entire inner space of the reflector with cooling air and the increase of the cooling effect. Accordingly, the invention disclosed in Patent Document 2is a means for cooling the entire inner space of the reflector and in no way achieves the object of reducing the temperature difference between the top portion and the bottom portion of the light source to extend the product life of the light source.